InstructionSimplify.cpp revision d06094f0682f2ede03caff4892b1a57469896d48 
1//===- InstructionSimplify.cpp - Fold instruction operands ----------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements routines for folding instructions into simpler forms
11// that do not require creating new instructions.  For example, this does
12// constant folding, and can handle identities like (X&0)->0.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/Analysis/InstructionSimplify.h"
17#include "llvm/Analysis/ConstantFolding.h"
18#include "llvm/Instructions.h"
19#include "llvm/Support/PatternMatch.h"
20using namespace llvm;
21using namespace llvm::PatternMatch;
22
23/// SimplifyAndInst - Given operands for an And, see if we can
24/// fold the result.  If not, this returns null.
25Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1,
26                             const TargetData *TD) {
27  if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
28    if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
29      Constant *Ops[] = { CLHS, CRHS };
30      return ConstantFoldInstOperands(Instruction::And, CLHS->getType(),
31                                      Ops, 2, TD);
32    }
33
34    // Canonicalize the constant to the RHS.
35    std::swap(Op0, Op1);
36  }
37
38  // X & undef -> 0
39  if (isa<UndefValue>(Op1))
40    return Constant::getNullValue(Op0->getType());
41
42  // X & X = X
43  if (Op0 == Op1)
44    return Op0;
45
46  // X & <0,0> = <0,0>
47  if (isa<ConstantAggregateZero>(Op1))
48    return Op1;
49
50  // X & <-1,-1> = X
51  if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
52    if (CP->isAllOnesValue())
53      return Op0;
54
55  if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
56    // X & 0 = 0
57    if (Op1CI->isZero())
58      return Op1CI;
59    // X & -1 = X
60    if (Op1CI->isAllOnesValue())
61      return Op0;
62  }
63
64  // A & ~A  =  ~A & A  =  0
65  Value *A, *B;
66  if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
67      (match(Op1, m_Not(m_Value(A))) && A == Op0))
68    return Constant::getNullValue(Op0->getType());
69
70  // (A | ?) & A = A
71  if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
72      (A == Op1 || B == Op1))
73    return Op1;
74
75  // A & (A | ?) = A
76  if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
77      (A == Op0 || B == Op0))
78    return Op0;
79
80  return 0;
81}
82
83/// SimplifyOrInst - Given operands for an Or, see if we can
84/// fold the result.  If not, this returns null.
85Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1,
86                            const TargetData *TD) {
87  if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
88    if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
89      Constant *Ops[] = { CLHS, CRHS };
90      return ConstantFoldInstOperands(Instruction::Or, CLHS->getType(),
91                                      Ops, 2, TD);
92    }
93
94    // Canonicalize the constant to the RHS.
95    std::swap(Op0, Op1);
96  }
97
98  // X | undef -> -1
99  if (isa<UndefValue>(Op1))
100    return Constant::getAllOnesValue(Op0->getType());
101
102  // X | X = X
103  if (Op0 == Op1)
104    return Op0;
105
106  // X | <0,0> = X
107  if (isa<ConstantAggregateZero>(Op1))
108    return Op0;
109
110  // X | <-1,-1> = <-1,-1>
111  if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
112    if (CP->isAllOnesValue())
113      return Op1;
114
115  if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
116    // X | 0 = X
117    if (Op1CI->isZero())
118      return Op0;
119    // X | -1 = -1
120    if (Op1CI->isAllOnesValue())
121      return Op1CI;
122  }
123
124  // A | ~A  =  ~A | A  =  -1
125  Value *A, *B;
126  if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
127      (match(Op1, m_Not(m_Value(A))) && A == Op0))
128    return Constant::getAllOnesValue(Op0->getType());
129
130  // (A & ?) | A = A
131  if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
132      (A == Op1 || B == Op1))
133    return Op1;
134
135  // A | (A & ?) = A
136  if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
137      (A == Op0 || B == Op0))
138    return Op0;
139
140  return 0;
141}
142
143
144
145
146static const Type *GetCompareTy(Value *Op) {
147  return CmpInst::makeCmpResultType(Op->getType());
148}
149
150
151/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
152/// fold the result.  If not, this returns null.
153Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
154                              const TargetData *TD) {
155  CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
156  assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
157
158  if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
159    if (Constant *CRHS = dyn_cast<Constant>(RHS))
160      return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
161
162    // If we have a constant, make sure it is on the RHS.
163    std::swap(LHS, RHS);
164    Pred = CmpInst::getSwappedPredicate(Pred);
165  }
166
167  // ITy - This is the return type of the compare we're considering.
168  const Type *ITy = GetCompareTy(LHS);
169
170  // icmp X, X -> true/false
171  if (LHS == RHS)
172    return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
173
174  if (isa<UndefValue>(RHS))                  // X icmp undef -> undef
175    return UndefValue::get(ITy);
176
177  // icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
178  // addresses never equal each other!  We already know that Op0 != Op1.
179  if ((isa<GlobalValue>(LHS) || isa<AllocaInst>(LHS) ||
180       isa<ConstantPointerNull>(LHS)) &&
181      (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
182       isa<ConstantPointerNull>(RHS)))
183    return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
184
185  // See if we are doing a comparison with a constant.
186  if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
187    // If we have an icmp le or icmp ge instruction, turn it into the
188    // appropriate icmp lt or icmp gt instruction.  This allows us to rely on
189    // them being folded in the code below.
190    switch (Pred) {
191    default: break;
192    case ICmpInst::ICMP_ULE:
193      if (CI->isMaxValue(false))                 // A <=u MAX -> TRUE
194        return ConstantInt::getTrue(CI->getContext());
195      break;
196    case ICmpInst::ICMP_SLE:
197      if (CI->isMaxValue(true))                  // A <=s MAX -> TRUE
198        return ConstantInt::getTrue(CI->getContext());
199      break;
200    case ICmpInst::ICMP_UGE:
201      if (CI->isMinValue(false))                 // A >=u MIN -> TRUE
202        return ConstantInt::getTrue(CI->getContext());
203      break;
204    case ICmpInst::ICMP_SGE:
205      if (CI->isMinValue(true))                  // A >=s MIN -> TRUE
206        return ConstantInt::getTrue(CI->getContext());
207      break;
208    }
209  }
210
211
212  return 0;
213}
214
215/// SimplifyFCmpInst - Given operands for an FCmpInst, see if we can
216/// fold the result.  If not, this returns null.
217Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
218                              const TargetData *TD) {
219  CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
220  assert(CmpInst::isFPPredicate(Pred) && "Not an FP compare!");
221
222  if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
223    if (Constant *CRHS = dyn_cast<Constant>(RHS))
224      return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
225
226    // If we have a constant, make sure it is on the RHS.
227    std::swap(LHS, RHS);
228    Pred = CmpInst::getSwappedPredicate(Pred);
229  }
230
231  // Fold trivial predicates.
232  if (Pred == FCmpInst::FCMP_FALSE)
233    return ConstantInt::get(GetCompareTy(LHS), 0);
234  if (Pred == FCmpInst::FCMP_TRUE)
235    return ConstantInt::get(GetCompareTy(LHS), 1);
236
237  if (isa<UndefValue>(RHS))                  // fcmp pred X, undef -> undef
238    return UndefValue::get(GetCompareTy(LHS));
239
240  // fcmp x,x -> true/false.  Not all compares are foldable.
241  if (LHS == RHS) {
242    if (CmpInst::isTrueWhenEqual(Pred))
243      return ConstantInt::get(GetCompareTy(LHS), 1);
244    if (CmpInst::isFalseWhenEqual(Pred))
245      return ConstantInt::get(GetCompareTy(LHS), 0);
246  }
247
248  // Handle fcmp with constant RHS
249  if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
250    // If the constant is a nan, see if we can fold the comparison based on it.
251    if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
252      if (CFP->getValueAPF().isNaN()) {
253        if (FCmpInst::isOrdered(Pred))   // True "if ordered and foo"
254          return ConstantInt::getFalse(CFP->getContext());
255        assert(FCmpInst::isUnordered(Pred) &&
256               "Comparison must be either ordered or unordered!");
257        // True if unordered.
258        return ConstantInt::getTrue(CFP->getContext());
259      }
260    }
261  }
262
263  return 0;
264}
265
266//=== Helper functions for higher up the class hierarchy.
267
268/// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
269/// fold the result.  If not, this returns null.
270Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
271                           const TargetData *TD) {
272  switch (Opcode) {
273  case Instruction::And: return SimplifyAndInst(LHS, RHS, TD);
274  case Instruction::Or:  return SimplifyOrInst(LHS, RHS, TD);
275  default:
276    if (Constant *CLHS = dyn_cast<Constant>(LHS))
277      if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
278        Constant *COps[] = {CLHS, CRHS};
279        return ConstantFoldInstOperands(Opcode, LHS->getType(), COps, 2, TD);
280      }
281    return 0;
282  }
283}
284
285/// SimplifyCmpInst - Given operands for a CmpInst, see if we can
286/// fold the result.
287Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
288                             const TargetData *TD) {
289  if (CmpInst::isIntPredicate((CmpInst::Predicate)Predicate))
290    return SimplifyICmpInst(Predicate, LHS, RHS, TD);
291  return SimplifyFCmpInst(Predicate, LHS, RHS, TD);
292}
293
294